SPERMATOGENESIS OF THE PIG. 13 



the autosomes, divide in this stage. A centrosphere containing 

 a tiny centrosome can be observed in some cases, but its presence 

 is not at discernible in these early cells as it is in the later stages. 



PRIMARY SPERMATOCYTES. 

 i. Resting Stage. 



The primary spermatocytes which arise from the final sperma- 

 togonial division in the early resting stage are usually somewhat 

 smaller than the spermatogonia in the metaphase and prophase 

 stages. The two large nucleoli are quite conspicuous and remain 

 black in sections stained with iron hematoxylin even in very 

 much destained material (Fig. 20). Usually two small nu- 

 cleoli, stained the same way as the large ones, are plainly visible 

 and occasionally only one, or more than two of these bodies 



appear. 



2. S'ynizesis and Growth Period. 



An increase in the bulk of both the nucleus and cytoplasm 

 begins after a brief period of rest. The chromatin appears to be 

 arranged in much the same w r ay as it was during the resting con- 

 dition of the spermatogonia, except that the linin fibers are 

 coarser. The cytoplasm is composed of granular masses and 

 clear, apparently liquid areas. The chromatin threads and 

 nucleoli become massed at one side of the nucleus (Fig. 21). The 

 nuclear wall expands and the clear area formed by the massing 

 of the chromatin to one side becomes much enlarged. The clear 

 areas in the cytoplasm decrease coincidentally with the increase 

 of the liquid-like area in the nucleus and one is led to believe 

 that the cytoplasmic fluid permeates the nuclear wall during the 

 period of synizesis. 



During the collapse of the chromatin material, the nucleoli 

 can be plainly seen especially in well destained sections (Fig. 21). 

 They are usually in that portion of the chromatin mass which is 

 nearest to the nuclear wall. Opposite this mass on the outside 

 of the nuclear wall a centrosphere can often be seen, but the 

 centrosome is rarely visible at this stage. The chromatin threads 

 become arranged in a very much tangled mass of loops which 

 later appear in about half the original number and fully twice as 

 thick. (I have not been able to determine definitely whether 



